1. Field of the Invention
The present invention relates to ways and means for the elimination of particulate pollutants from combustion gases and, more particularly, to a method of removing soot from exhaust gases of internal combustion engines, especially diesel engines, wherein the soot particles are filtered out of the exhaust gas flow and combusted with the aid of combustion-inducing substances.
2. Description of the Prior Art
In U.S. Pat. No. 4,436,535 to H. Erdmannsdorfer, M. Wagner and G. Weyh is disclosed a method and device for removing soot from the exhaust gases of an internal combustion engine, especially of the diesel-type, featuring a soot filter in the exhaust line and a dosing device which injects a dose of a combustion-inducing substance, preferably copper(I) chloride (CuCl), into the soot filter with the aid of a flow of compressed air.
The soot combustion process is initiated automatically, in response to the presence of a critical level of counter-pressure in the exhaust filter and the simultaneous presence of a sufficiently high temperature inside the soot filter. The critical pressure level is ascertained by means of a pressure switch and the critical temperture is monitored with a temperature probe which controls a thermal switch. The two switches are connected in series.
Following the air-carried injection of a dose of the combustion-inducing substance into the filter, additional compressed air is injected into the soot filter, through a line which bypasses the supply container, in order to supply additional oxygen for the combustion of the accumulated soot. This bypass flow also serves to scavenge the supply line downstream of the supply container.
Through the addition of copper(I) chloride, it is possible to lower the ignition temperature of the soot layer on the filter cartridge to approximately 350.degree. Celsius. It thus becomes possible to burn off the soot without applying supplemental heat to the exhaust flow upstream of the soot filter, or directly to the soot layer, as was necessary before that. The result is not only a considerable saving in energy requirements, but also a marked lowering in the thermal stress to which the filter cartridge is subjected during the soot combustion process.
Practical experience with this prior solution under the most varied operating conditions has revealed that even the greatly lowered ignition temperature of 350.degree. Celsius cannot always be reached in the soot filter with sufficient certainty. Such a situation may accur at very low ambient temperatures and/or when the internal combustion engine is operated for an extended period of time under low partial load, or when a supercharger is employed.
Another shortcoming of this known solution is the fact that small amounts of copper oxide are precipitated out of the combustion-induding copper(I) chloride. And, with the passage of operating time, a coating of copper oxide forms on the filter cartridge, which becomes a drawback to the efficient operation of the engine by increasing the flow resistance of the soot filter.